Revisiting the Concept of Activation in Supercooled Liquids

Abstract

In this work we revisit the description of dynamics based on the concepts of metabasins and activation in mildly supercooled liquids via the analysis of the dynamics of a paradigmatic glass former between its onset temperature To and mode-coupling temperature Tc. First, we provide measures that demonstrate that the onset of glassiness is indeed connected to the landscape, and that metabasin waiting time distributions are so broad that the system can remain stuck in a metabasin for times that exceed τα by orders of magnitude. We then reanalyze the transitions between metabasins, providing several indications that the standard picture of activated dynamics in terms of traps does not hold in this regime. Instead, we propose that here activation is principally driven by entropic instead of energetic barriers. In particular, we illustrate that activation is not controlled by the hopping of high energetic barriers, and should more properly be interpreted as the entropic selection of nearly barrierless but rare pathways connecting metabasins on the landscape.

Relaxation dynamics in the energy landscape of glass-forming liquids

“…However, these approaches do not have the same level of rigor as those in p-spin models since inherent structures are different from pure states [19,24,25]. The structure of the potential energy landscape and its precise relationship with dynamics and thermodynamics remain under intense scrutiny [8,26]. In particular, the role of excitations in the potential energy landscape has been discussed in connection with sound propagation [27], specific heat [28], vibrational [29] and mechanical properties [30].…”

Finite size effects and loss of self-averageness in the relaxational dynamics of the spherical Sherrington–Kirkpatrick model

“…These studies were boosted by the will to better grasp the relaxation of glassy systems but they are obviously very important for applications beyond physics, where the number of degrees of freedom can be large but definitely not diverge. Most importantly, the main goals of these recent studies were to distinguish the relaxation akin to gradient descent from activation over free-energy barriers and, especially, to quantify the role played by the latter in the approach to equilibrium [11][12][13][14][15][16] (see also [17][18][19] from the mathematics literature).…”

Finite size effects and loss of self-averageness in the relaxational dynamics of the spherical Sherrington-Kirkpatrick model

“…These studies were boosted by the will to better grasp the relaxation of glassy systems. Most importantly, the goals were to distinguish the relaxation akin to gradient descent from activation over free-energy barriers and, especially, to quantify the role played by the latter in the approach to equilibrium [11,12,13,14,15,16] (see also [17,18,19] from the mathematics literature).…”